Erythrite

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(Redirected from Cobalt bloom)
Erythrite
Erythrite crystals
General
CategoryArsenate mineral
Formula
(repeating unit)
Co3(AsO4)2·8H2O
IMA symbolEry[1]
Strunz classification8.CE.40
Dana classification40.03.06.03
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/m
Identification
ColorCrimson to peach-red, pale rose, or pink, may be zoned
Crystal habitRadial or stellate aggregates, fibrous, drusy; usually powdery and massive – rarely as striated prismatic crystals
CleavagePerfect on {010}; poor on {100} and {102}.
TenacitySectile
Mohs scale hardness1.5–2.5
LusterSubadamantine, pearly on cleavages
StreakPale red to pink
DiaphaneityTransparent to translucent
Specific gravity3.06
Optical propertiesBiaxial (+)
Refractive indexnα = 1.626 – 1.629 nβ = 1.662 – 1.663 nγ = 1.699 – 1.701
Birefringenceδ = 0.073
PleochroismVisible: X = pale pinkish to pale rose; Y = pale violet to pale violet-rose; Z = deep red
References[2][3][4]

Erythrite or red cobalt is a secondary hydrated cobalt arsenate mineral with the formula Co
3
(AsO
4
)
2
•8H
2
O
. Erythrite and annabergite, chemical formula Ni
3
(AsO
4
)
2
•8H
2
O
, or nickel arsenate form a complete series with the general formula (Co,Ni)
3
(AsO
4
)
2
•8H
2
O
.

Erythrite from Morocco

Erythrite crystallizes in the monoclinic system and forms prismatic crystals. The color is crimson to pink and occurs as a secondary coating known as cobalt bloom on cobalt arsenide minerals. Well-formed crystals are rare, with most of the mineral manifesting in crusts or small reniform aggregates.

Erythrite was first described in 1832 for an occurrence in Grube Daniel, Schneeberg, Saxony,[4] and takes its name from the Greek έρυθρος (erythros), meaning red.[3] Historically, erythrite itself has not been an economically important mineral, but the prospector may use it as a guide to associated cobalt and native silver.[citation needed]

Erythrite occurs as a secondary mineral in the oxide zone of Co–Ni–As bearing mineral deposits. It occurs in association with cobaltite, skutterudite, symplesite, roselite-beta, scorodite, pharmacosiderite, adamite, morenosite, retgersite, and malachite.[2]

Notable localities are Cobalt, Ontario; La Cobaltera, Chile, Schneeberg, Saxony, Germany; Joachimsthal, Czech Republic; Cornwall, England; Bou Azzer, Morocco; the Blackbird mine, Lemhi County, Idaho; Sara Alicia mine, near Alamos, Sonora, Mexico; Mt. Cobalt, Queensland and the Dome Rock copper mine, Mingary, South Australia.[2]

Other varieties[edit]

The nickel variety, annabergite, occurs as a light green nickel bloom on nickel arsenides. In addition iron, magnesium and zinc can also substitute for the cobalt position, creating three other minerals: parasymplesite (Fe), hörnesite (Mg) and köttigite (Zn).

References[edit]

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ a b c Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (2005). "Erythrite" (PDF). Handbook of Mineralogy. Mineral Data Publishing. Retrieved 27 July 2022.
  3. ^ a b Erythrite, Mindat.org, retrieved 27 July 2022
  4. ^ a b Barthelmy, David (2014). "Erythrite Mineral Data". Webmineral.com. Retrieved 27 July 2022.

Further reading[edit]